The objectives of this project are to determine the physiological mechanisms and functional significance of age-related changes in circadian rhythms and sleep and to examine the feasibility and efficacy of corrective strategies. Our long-term goal is to enhance the health and life quality of older adults by improving nocturnal sleep, decreasing daytime sleepiness and re-establishing the hormonal correlates of a normal sleep-wake cycle. This multidisciplinary project combines the efforts of investigators at the University of Chicago and at Northwestern University and includes non- invasive studies in subjects in assisted living facilities, Clinical Research Center studies of middle-aged and older adults, in vivo studies of circadian rhythmicity and sleep in hamsters and rats and in vitro molecular studies. Project #1 will determine whether the timings of photic and activity exposure are critical for their beneficial effects and explore the efficacy of strategies increasing the magnitude of non-photic inputs to consolidate sleep and improve daytime function in nursing home residents. Project #2 will test the hypothesis that midlife decreases in both non- photic and photic inputs to the circadian system may contribute to the development of alterations of circadian function, sleep and endocrine function in late life as well as explore strategies designed to restore exposure to non-photic and photic inputs to correct such alterations in midlife and late life. Project #3 will determine the chronology of age- related changes in the circadian system, test hypotheses regarding the role of Neuropeptide Y in causing alterations in non-photic inputs and explore corrective strategies involving increased exposure to both photic and non- photic inputs in hamsters. Project #4 will investigate the effect s of aging on the neural and molecular mechanisms subserving photic entrainment and examine the role of genetic factors in age-related changes in expression of circadian rhythmicity. Project #5 will determine the roles of age-related alterations in circadian rhythmicity and pineal function in causing sleep disturbances in rats. These five Project will be supported by three Cores. Core A (Administrative) will provide the overall logistical and financial coordination and assist in the recruitment of older volunteers. Core B (Methods and Analysis) will supply, operate and maintain the equipment used in the five Projects to monitor circadian rhythms and sleep in humans and rodents and provide methods for reporting and analyzing profiles of behavioral and physiological variables. Core C (Laboratory ) will assay blood and/or saliva levels of hormones for Projects #1, #2 and #3.